Method of integration of a magnetoresistive structure

ABSTRACT

A method of manufacturing one or more interconnects to a magnetoresistive structure, the method comprising depositing a first conductive material (i) in a via which is formed through a first surface of a first dielectric layer and (ii) directly on the first surface of the first dielectric layer. The method further includes etching the first conductive material wherein, after etching the first conductive material, a portion of the first conductive material remains (i) in the via and (ii) directly on the first surface of the first dielectric layer. The method also includes partially filling the via by depositing a second conductive material (i) in the via and (ii) directly on the first conductive material remaining in the via, depositing a first electrode material (i) in the via and (ii) directly on the second conductive material which is in the via, and forming a magnetoresistive structure over the first electrode material.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/704,915, filed May 5, 2015 (now U.S. Pat. No. 9,553,260), which is acontinuation of U.S. patent application Ser. No. 13/328,874, filed Dec.16, 2011 (U.S. Pat. No. 9,054,297). This non-provisional application,the '915 application, and the '874 application claim priority to and thebenefit of U.S. Provisional Application No. 61/424,359, filed Dec. 17,2010.

TECHNICAL FIELD

The exemplary embodiments described herein generally relate tomagnetoelectronics information devices and more particularly to magneticrandom access memories.

BACKGROUND

Magnetoelectronic devices, spin electronic devices, and spintronicdevices are synonymous terms for devices that make use of effectspredominantly caused by electron spin. Magnetoelectronics are used innumerous information devices to provide non-volatile, reliable,radiation resistant, and high-density data storage and retrieval. Thenumerous magnetoelectronics information devices include, but are notlimited to, Magnetoresistive Random Access Memory (MRAM), magneticsensors, and read/write heads for disk drives.

Typically an MRAM includes an array of magnetoresistive memory elements.Each magnetoresistive memory element typically has a structure thatincludes multiple magnetic layers separated by various non-magneticlayers, such as a magnetic tunnel junction (MTJ), and exhibits anelectrical resistance that depends on the magnetic state of the device.Information is stored as directions of magnetization vectors in themagnetic layers. Magnetization vectors in one magnetic layer aremagnetically fixed or pinned, while the magnetization direction ofanother magnetic layer may be free to switch between the same andopposite directions that are called “parallel” and “antiparallel”states, respectively. Corresponding to the parallel and antiparallelmagnetic states, the magnetic memory element has low and high electricalresistance states, respectively. Accordingly, a detection of theresistance allows a magnetoresistive memory element, such as an MTJdevice, to provide information stored in the magnetic memory element.There are two completely different methods used to program the freelayer: field-switching and spin-torque switching. In field-switchedMRAM, current carrying lines adjacent to the MTJ bit are used togenerate magnetic fields that act on the free layer. In spin-torqueMRAM, switching is accomplished with a current pulse through the MTJitself. The spin angular momentum carried by the spin-polarizedtunneling current causes reversal of the free layer, with the finalstate (parallel or antiparallel) determined by the polarity of thecurrent pulse. The memory elements are programmed by the magnetic fieldcreated from current-carrying conductors. Typically, twocurrent-carrying conductors, the “digit line” and the “bit line”, arearranged in cross point matrix to provide magnetic fields forprogramming of the memory element. Because the digit line usually isformed underlying the memory element so that the memory element may bemagnetically coupled to the digit line, the interconnect stack thatcouples the memory element to the transistor typically is formed, usingstandard CMOS processing, offset from the memory element.

The interconnect stack is formed utilizing a number of vias andmetallization layers. The via that electrically couples the interconnectstack to the memory element often is referred to as the MVia. Presentday methods for forming MVias in an MRAM device often produceundesirable results and challenges. For example, the MVia is positionedadjacent to the interconnect stack and connected thereto by a digit linelanding pad, which typically is formed at the same time the digit lineis formed.

Efforts have been ongoing to improve scaling, or density, of MTJelements in an MRAM array. However, such efforts have included methodsthat use multiple masking and etching steps that consume valuable realestate in the MRAM device. Because an MRAM device may include millionsof MTJ elements, such use of real estate in the formation of each MTJelement can result in a significant decrease in the density of the MRAMdevice.

Accordingly, it is desirable to provide a process for manufacturing amagnetic random access memory that provides improved scaling.Furthermore, other desirable features and characteristics of theexemplary embodiments will become apparent from the subsequent detaileddescription and the appended claims, taken in conjunction with theaccompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

Methods and structures are described for manufacturing amagnetoresistive memory element having a conductive via, for connectingbetween a digit line and one side of the magnetoresistive memoryelement, positioned beneath, and aligned with, each magnetoresistivememory element. Other contacts on an array of the magnetoresistivememory elements may satisfy the same design rules, using the sameprocess step.

In accordance with a first exemplary embodiment, a method ofmanufacturing a magnetic element, the method comprises forming a firstvia in a first dielectric material; forming a first conductive materialin the first via, wherein the first conductive material creates a stepfunction with the first dielectric layer, the step function having amagnitude; reducing the magnitude of the step function; and forming amagnetic tunnel junction over, and aligned with, the first via.

A second exemplary embodiment includes a method of manufacturing amagnetic element, the magnetic element comprising etching a via througha first dielectric layer; forming a first conductive material in thefirst via; forming a first electrode on, and having a first surfaceopposed to, the first conductive material and the first dielectriclayer; polishing the first surface; and forming a magnetic tunneljunction on the first surface, the magnetic tunnel junction alignedwith, and in electrical contact with, the first conductive material.

A third exemplary embodiment includes a method of manufacturing amagnetic element, comprising etching a first via through a firstdielectric layer; forming a first conductive material in the first via;etching a portion of the first conductive material; forming a secondconductive material over the first conductive material remaining in thefirst via; forming a first electrode over the second conductivematerial; and forming a magnetic tunnel junction over the firstelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIGS. 1-4 are cross sections of a magnetoresistive memory elementmanufactured in accordance with a first exemplary embodiment;

FIG. 5 is a flow chart in accordance with an exemplary process formanufacturing the magnetoresistive memory element of FIGS. 1-4;

FIG. 6 is a cross section of an array of magnetoresistive memoryelements including a contact via in accordance with a second exemplaryembodiment;

FIG. 7 is a flow chart in accordance with an exemplary process formanufacturing the magnetoresistive memory array of FIG. 6;

FIG. 8 is a cross section of a magnetoresistive memory elementmanufactured in accordance with a third exemplary embodiment;

FIGS. 9-12 are cross sections of a magnetoresistive memory elementmanufactured in accordance with a fourth exemplary embodiment;

FIG. 13 is a flow chart in accordance with an exemplary process formanufacturing the magnetoresistive memory element of FIGS. 9-12;

FIGS. 14-17 are cross sections of an exemplary process for filling a viain the magnetoresistive memory elements of FIGS. 1-4, 6, 8, and 9-12;and

FIG. 18 is a flow chart in accordance with an exemplary process forfilling the via of FIGS. 14-17.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. Any implementation describedherein as exemplary is not necessarily to be construed as preferred oradvantageous over other implementations. Furthermore, there is nointention to be bound by any expressed or implied theory presented inthe preceding technical field, background, brief summary, or thefollowing detailed description.

In general, methods and structures are described for manufacturing amagnetoresistive memory element, e.g., a magnetic tunnel junction (MTJ)device. A conductive via for connecting between a digit line and oneside of the magnetic device is positioned beneath, and aligned with,each magnetic device. Other contacts may satisfy the same design rules,using the same process step. This integration approach allows forimproved scaling the MRAM devices to at least a 45 nanometer node and acell packing factor approaching 6 F². Without implementing the on-axisvia, the cell packing factor must be greater than 20 F².

During the course of this description, like numbers are used to identifylike elements according to the different figures that illustrate thevarious exemplary embodiments.

For simplicity and clarity of illustration, the drawing figures depictthe general structure and/or manner of construction of the variousembodiments. Descriptions and details of well-known features andtechniques may be omitted to avoid unnecessarily obscuring otherfeatures. Elements in the figures are not necessarily drawn to scale:the dimensions of some features may be exaggerated relative to otherelements to assist improve understanding of the example embodiments.

Terms of enumeration such as “first,” “second,” “third,” and the likemay be used for distinguishing between similar elements and notnecessarily for describing a particular spatial or chronological order.These terms, so used, are interchangeable under appropriatecircumstances. The embodiments of the invention described herein are,for example, capable of use in sequences other than those illustrated orotherwise described herein.

As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises a list ofelements does not include only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. The term “exemplary” is used in the sense of“example,” rather than “ideal.”

In the interest of conciseness, conventional techniques, structures, andprinciples known by those skilled in the art may not be describedherein, including, for example, standard magnetic random access memory(MRAM) process techniques, fundamental principles of magnetism, andbasic operational principles of memory devices.

During fabrication of an MRAM array architecture, each succeeding layeris deposited or otherwise formed in sequence and each MTJ device may bedefined by selective deposition, photolithography processing, etching,etc. using any of the techniques known in the semiconductor industry.Typically the layers of the MTJ are formed by thin-film depositiontechniques such as physical vapor deposition, including magnetronsputtering and ion beam deposition, or thermal evaporation.

Magnetoresistance is the property of a material to change the value ofits electrical resistance depending on its magnetic state. Typically,for a structure with two ferromagnetic layers separated by a conductiveor tunneling spacer, the resistance is highest when the magnetization ofthe second magnetic layer is antiparallel to that of the first magneticlayer, and lowest when they are parallel.

FIGS. 1-4 illustrate a process for manufacturing a magnetoresistivememory device 100, including a magnetic bit 102 (magnetic tunneljunction). In practice, an MRAM architecture or array will include manyMRAM devices 100, typically organized in a matrix of columns and rows.In forming each magnetoresistive memory device, a via 104 is etched in adielectric layer 106 and a conductive material 108 is deposited withinthe via 104. Dielectric material 106, as well as any other dielectricmaterial mentioned hereafter, may be formed of any suitable dielectricmaterial, for example, silicon dioxide. The conductive material 108 maybe fabricated using well known CMOS processes, such as damasceneprocessing or subtractive pattern processing such as etching, andpreferably comprise tantalum (Ta), tungsten (W), or ruthenium (Ru), butmay comprise any suitable conductive material, such as aluminum (Al),aluminum alloys, copper (Cu) and copper alloys and may include barriermaterials such as, for example, tantalum (Ta), tantalum nitride (TaN),titanium (Ti), titanium nitride (TiN), or titanium tungsten (TiW). Theconductive material 108 may be electrically coupled to a transistorformed in a semiconductor substrate as described in more detail insubsequent embodiments.

However, the deposition of the conductive material 108 in the via 104may create a “step function” 110, which is a difference in the level(dimension having a magnitude) of the surface 112 of the dielectricmaterial 106 and the surface 114 of the conductive material 108. Thesurface 114 of the conductive material 108 may be above or below thesurface 112 of the dielectric material 106. Additionally, the depositionof the conductive material may create a “seam” 116, or opening,vertically within the conductive material 108. Both the step functionand seam create uneven surfaces that are propagated upward during thesubsequent forming of additional layers above the via 104.

In accordance with the exemplary embodiment, an electrode 122 isdeposited on the dielectric layer 106 and the via including theconductive material 108, generally filling in the step function 110 andthe seam 116 (FIG. 2). Note that the “defects” 124 are propagated to thetop surface 126 of the electrode 122. In order to eliminate this upwardpropagation of these defects, a polish, or smoothing, of the top surface124 is performed resulting in a smooth surface 128 (FIG. 3).

Referring to FIG. 4, the magnetic bit 102 is formed over the conductivematerial 108 in the via 104. The magnetic bit 102 includes a tunnelbarrier 132 formed between a fixed layer 134 and a free layer 136. Thetunnel barrier 132 may be a dielectric, typically an oxide such as MgOor AlOx. The position of the fixed layer 134 and the free layer 136 maybe reversed. Another electrode 138 is deposited on the free layer 136. Ametal contact layer 140 is optionally deposited on the electrode 138 forcontact to a metal layer (not shown). While a three layer magnetic bit102 is shown, various other types of magnetic bits, including forexample spin torque, dual tunnel barrier, dual spin filter, and fieldswitching devices may be used with the present invention.

The first and second electrodes 122, 138 are formed from any suitablematerial capable of conducting electricity. For example, electrodes 122,138 may be formed from at least one of the elements Al, Cu, Ta, TaNx, Tior their combinations. The various ferromagnetic layers 134, 136including those in electrodes 122, 138 as known to those skilled in theart may comprise any suitable material having the desired ferromagneticproperties as described above.

In practice, MRAM device 100 may employ alternative and/or additionalelements, and one or more of the elements depicted in FIG. 4 may berealized as a composite structure or combination of sub-elements. Thespecific arrangement of layers shown in FIG. 4 merely represents onesuitable embodiment of the invention.

The via 104 is placed below the magnetic bit 102 for coupling the bottomelectrode 122 directly or indirectly to a transistor source or drain(not shown). The via 104 is below and aligned with the magnetic bit 102,thereby eliminating additional conducting lines if the via were placedbeside the magnetic bit; thereby improving scaling and cell packing(density).

For the purposes of clarity, some commonly-used layers have not beenillustrated in the drawings, including various protective cap layers,seed layers, and the underlying substrate (which may be a conventionalsemiconductor substrate or any other suitable structure). For theexemplary embodiments shown, the bottom electrode 122 is a ferromagneticpolarizer, while the top electrode 138 may be either a non-ferromagneticmaterial or a ferromagnetic polarizer. Alternatively, only the topelectrode 138 may be a ferromagnetic polarizer. Generally, aferromagnetic polarizer would include a pinning layer, a pinned magneticlayer, a coupling spacer layer, and a fixed magnetic layer adjacent tothe tunnel barrier 132 (none of which are shown in FIG. 4) as is wellknown in the industry.

Referring to FIG. 5, the steps of forming the magnetic bit 102 over thevia 104 include forming 502 the dielectric layer 106 and etching 504 avia 104 through the dielectric layer 106. A conductive material 108 isformed 506 in the via 104, and an electrode 122 is formed 508 on, andhaving a surface 126 opposed to, the conductive material 108 and thedielectric layer 106. A polishing 510 of the surface 126 is performedand a magnetic bit 102 is formed 512 on the surface. Therefore, themagnetic bit 102 is aligned with, and in electrical contact with, theconductive material 108 within the via 104.

Referring to FIG. 6, an array of the magnetoresistive devices 100 areformed between a dielectric layer 602 and a metal line 604. Though onlyone magnetoresistive device 100 is shown, the number of magnetoresistivedevices 100 could be up to the gigabit range. The conductive material108 within the via 104 is formed over a transistor 606 includingconducting electrodes 607, 608 and a gate 609. More specifically, theconductive material 108 is in contact with the conducting electrode 608.Another transistor 616, including conducting electrodes 617, 618 andgate 619 is formed in the dielectric layer 602. In order to provide aconnection from the transistor 616 (specifically the conductingelectrode 618 as shown) to the metal line 604, a contact 622 is formed(during the same process step with via 104 (FIG. 1)) in the dielectriclayer 106 and a conductive material 624 is deposited therein. Aconductive via 628 is then formed above the contact 622 for coupling tothe metal line 604. This architecture allows positioning the magneticbit below the first metal layer. With this selection, it is possible todesign the bitcell to avoid use of additional connections down to theunderlying transistor in every bitcell, thereby enabling shrinkage ofthe bitcell to a cell factor of 6 F².

The process for forming this array of magnetoresistive memory devicesincludes the steps of (FIG. 7) etching 702 a plurality of vias 104, 622through a first dielectric layer and forming 704 a conductive material108, 624 in the vias 104, 622. For each of the magnetoresistive memorydevices 100, a first contact is formed 706 on the first conductivematerial 108 in the first via and a second contact 622 on the secondconductive material. A first electrode is formed 708 on, and having asurface opposed to, the conductive material 108. The surface is polished710, and a magnetic bit is formed 712 on the surface, wherein themagnetic bit is aligned with, and in electrical contact with, theconductive material 108 in the via 104. At the time of forming theconductive material 108 for the magnetoresistive memory devices 100, theadditional contact 624 is formed 706 in the dielectric material 106 butdisplaced from the magnetoresistive memory devices 100. A conductive via628 is then formed 714 above the contact 622 for coupling to the metalline 604. Typically the metal layer 604 is formed over both the thirdconductive material 628 and the magnetic bit 102.

Alternatively, referring to FIG. 8, the magnetoresistive memory element100 of FIG. 4 may be formed above the metal line 604 (FIG. 6), which maybe any metal layer.

In addition to the process steps and advantages thereof mentioned above,a chemical mechanical polish (CMP) process may be performed to allow fora thinner upper electrode. Referring to FIG. 9, a polish stop layer 902of a dielectric material is deposited over the magnetic bit 102 and thedielectric layer 106. A dielectric layer 904 is deposited over thepolish stop layer 902. A polish, preferably a CMP, is performed toremove the dielectric layer above the magnetic bit 102 (FIG. 10). Anetch stop layer 906 is deposited over the polish stop layer 902 and thedielectric layer 904, and a dielectric layer 908 is deposited over theetch stop layer 906 (FIG. 11). An etch is performed to remove thedielectric layer 908 above the magnetic bit and another etch isperformed to remove the etch stop layer 904 and the polish stop layer902 over the magnetic bit 102. A metal 912 is then formed within theopening above, and in contact with, the magnetic bit 102 (FIG. 12).

FIG. 13 is a flow chart of the steps of the CMP process, includingforming 1302 a CMP stop layer 902 over the first dielectric layer 106and the magnetic bit 102. A second dielectric layer 904 is deposited1304 over the CMP stop layer 902. A polish is performed 1306 to removethe second dielectric layer 904 to the CMP stop layer 902. An etch stoplayer 906 is deposited 1308 on the CMP stop layer 902 and a thirddielectric layer 908 is formed 1310 over the etch stop layer 906. Anopening 912 is then etched 1312 through the third dielectric layer 908,the etch stop layer 906, and the CMP stop layer 902 to expose themagnetic bit 102. A conductive material 912 is formed 1314 on themagnetic bit 102 within the opening 912.

Yet additional improvements may be made to the process for manufacturingthe magnetoresistive memory device 100 by filling the via 104 by adeposition-etch-deposition process, that may be performed in-situ(within the same chamber or on the same platform without breakingvacuum). FIGS. 14-17 are cross sectional drawings illustrating theprocess, which is shown in the flow chart of FIG. 18. A first metal 1402is deposited 1802 in the via 104. An etch is performed 1804 to remove afirst portion of the first metal 1402 while leaving a second portion1502 within the via 104. A second metal 1602 is formed 1806 over thesecond portion 1502, including within the via 104 (FIG. 16). Theelectrode 122 (see FIG. 2-4) is deposited 1608 over the second metal1602, resulting in a smoother “filling” of the via 104. A polishing ofthe electrode may then be performed as discussed above. Optionally, moreof the material of the electrode 122 may be deposited over the electrode122 subsequent to the polishing.

Although the described exemplary embodiments disclosed herein aredirected to various semiconductor memories and methods for making same,the present invention is not necessarily limited to the exemplaryembodiments which illustrate inventive aspects of the present inventionthat are applicable to a wide variety of semiconductor processes and/ordevices. Thus, the particular embodiments disclosed above areillustrative only and should not be taken as limitations upon thepresent invention, as the invention may be modified and practiced indifferent but equivalent manners apparent to those skilled in the arthaving the benefit of the teachings herein. For example, the relativepositions of the free and pinning layers in a memory structure may bereversed so that the pinning layer is on top and the free layer isbelow. Also the free layers and the pinning layers may be formed withdifferent materials than those disclosed. Moreover, the thickness of thedescribed layers may deviate from the disclosed thickness values.Accordingly, the foregoing description is not intended to limit theinvention to the particular form set forth, but on the contrary, isintended to cover such alternatives, modifications and equivalents asmay be included within the spirit and scope of the invention as definedby the appended claims so that those skilled in the art shouldunderstand that they can make various changes, substitutions andalterations without departing from the spirit and scope of the inventionin its broadest form.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims.

A number of embodiment have been presented in the foregoing detaileddescription. It should be appreciated that the exemplary embodiment orexemplary embodiments are only examples, and are not intended to limitthe scope, applicability, or configuration of the invention in any way.Rather, the foregoing detailed description will provide those skilled inthe art with a convenient road map for implementing an exemplaryembodiment of the invention, it being understood that various changesmay be made in the function and arrangement of elements described in anexemplary embodiment without departing from the scope of the inventionas set forth in the appended claims.

What is claimed is:
 1. A method of manufacturing one or moreinterconnects to a magnetoresistive structure, the method comprising:depositing a first conductive material (i) in a via which is formedthrough a first surface of a first dielectric layer and (ii) directly onthe first surface of the first dielectric layer; etching the firstconductive material wherein, after etching the first conductivematerial, a portion of the first conductive material remains (i) in thevia and (ii) directly on a portion of the first surface of the firstdielectric layer; partially filling the via by depositing a secondconductive material (i) in the via and (ii) directly on the firstconductive material remaining in the via; depositing a first electrodematerial (i) in the via and (ii) directly on the second conductivematerial which is in the via; and forming a magnetoresistive structureover the first electrode material.
 2. The method of claim 1 whereindepositing the first conductive material, etching a portion of the firstconductive material, and depositing the second conductive material areperformed in-situ.
 3. The method of claim 1 wherein: the firstconductive material comprises tantalum or tantalum-nitride, and thefirst electrode material comprises tantalum or tantalum-nitride.
 4. Themethod of claim 1 wherein the magnetoresistive structure is a magneticbit.
 5. The method of claim 4 wherein depositing the first conductivematerial, etching the first conductive material, and depositing thesecond conductive material are performed in-situ.
 6. The method of claim1 wherein the method further includes depositing a second electrodematerial directly on the first electrode material, and wherein forming amagnetoresistive structure over the first electrode material includesforming a magnetoresistive structure directly on the second electrodematerial.
 7. The method of claim 1 wherein depositing the secondconductive material further includes depositing the second conductivematerial directly on the first conductive material that is locateddirectly on the portion of the first surface of the first dielectriclayer.
 8. The method of claim 1 wherein the method further includespolishing a first surface of the first electrode material.
 9. The methodof claim 8 wherein, after polishing the first surface of the firstelectrode material, the method further includes depositing a secondelectrode material directly on the first electrode material, and whereinforming a magnetoresistive structure over the first electrode materialincludes forming a magnetoresistive structure directly on the secondelectrode material.
 10. The method of claim 9 wherein forming amagnetoresistive structure over the first electrode material includesforming a magnetoresistive structure directly on the second electrodematerial.
 11. The method of claim 1 wherein depositing the firstconductive material, etching a portion of the first conductive material,and depositing the second conductive material are performed in-situ, andwherein the method further includes: polishing a first surface of thefirst electrode material.
 12. The method of claim 11 wherein, afterpolishing the first surface of first electrode material, the methodfurther includes depositing a second electrode material directly on thefirst electrode material, and wherein forming a magnetoresistivestructure over the first electrode material includes forming amagnetoresistive structure directly on the second electrode material.13. The method of claim 1 wherein the method further includes depositinga second electrode material directly on the first electrode material.